Treating thiocyanates



Patented Sept. 20, 1932 UNITED STATES PATENT 'FFlCE CHRISTIAN J. HANSEN,OF ESSEN-RUHR, GERMANY, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO THEIKOPIERS COMPANY OF DELAWARE, OF PITTSBURGH, PENNSYL- VANIA, ACORPORATION OF DELAWARE TREATING THIOGYANATES .No Drawing. Originalapplication filed August 9, 1928, Serial No. 298,617, and in GermanyApril 14, 1928. Divided and this application filed November 29, 1929.Serial No. 410,650.

'My invention refers to the treatment of thiocyanogen compounds and moreespecially ammonium thiocyanate, whereby a decomposition of suchcompounds is obtained and sulfur and the corresponding sulfates, such asammonium sulfate, are recovered. It is an object of my invention toprovide means whereby this decomposition of the thiocyanogen compoundsand conversion into sulfates and free sulfur can be eflected in asimpler and more efficient manner and at lower cost, than was hithertopossible.

Hitherto solutions of ammonium thiocyanate, such as resulted forinstance in the purification of gases developed in the distillation ofcarbon and other carbonaceous material, have been subjected tohydrolitic decomposition by heating same with acids, more especiallywith dilute sulfuric acid. This decomposition results in the formationof ammonium sulfate and carbon oxysulfide, which is partly decomposed inthe presence of wa ter into carbon dioxide and hydrogen sulfide. ThisWay of proceeding entails the drawback that it requires a considerableoutlay for the sulfuric acid required in the decomposition, and thesulfur compounds resulting in the reaction must be subjected separatelyto further treatment.

In my copending application, Serial No. 298,617, filed August 9, 1928, Ihave described a generally applicable method of decomposing thiocyanatesand of forming ammonium compounds therefrom by heating an aqueoussolution of such thiocyanates in the presence of compounds containingthe radical S0 According to the present invention the thiocyanatescontained in the coal distillation gases can be converted into ammoniumsulfate and free sulfur in a particularly simple and effective manner.No addition of further reagents such as sulfuric acid is required, andthe ammonium thiocyanate is rapidly converted in a single operation intoammonium sulfate and free sulfur.

I have ascertained that if ammonium thiocyanate or other thiocyanatesare heated in the instantaneous and continuous absorption by thebisulfite not only of the ammonia, but

also of the hydrogen sulfide developed in the hydrolytic reactionmentioned above.

It is well known that a complete decomposition of bisulfite and sulfiteinto sulfate and free sulfur requires predetermined proportions of theseveral constituents, i. e. that for each two molecules of a bisulfiteone molecule of sulfur must be present. If the quantities of sulfite insolution are greater, complete decomposition is not possible inasmuch asin that case the solution contains besides sulfate also non-decomposedsulfide. If there is bisulfite in excess in the solution, there isformed, when operating in closed vessels, besides ammonium sulfate acorresponding quantity of free sulfuric acid.

Before going into the details of my invention and how the same iscarried out in practice, I will first explain the facts on which thisinvention is based. I

1 First of all I found that ammonium thiocyanate can be decomposed in aquantitative manner by heating an aqueous solution thereof with sulfurdioxide, ammonium bisulfite or ammonium thiosulfate in combination withsulfur dioxide. 7 y

The following equation serves to illustrate this decomposition.

This reaction can be explained as follows:

The decomposition of thiocyanic acid occurs according to the equation:

II. HCNS+H O =NH +COS Carbon oxysulfide is further decomposed in sulfurdioxide, the reaction occurs contact with wateraccording to theequation:

III. COS +H O CO +I-I S Thus from lHCNS is finally formed lNH and 1H S.

If ammonium thiocyanate is treated in this way, QNH and lH S willresult.

' In order to produce 1(NI-I from NILCNS, the sulfur dioxide must firstbe converted into S0 according to the equation:

Therefore inord'er to obtain 1SO 1.5SO is required, which results in lSO+0.5S. 7

Further in order to convert the hydrogen sulfide obtained in thedecomposition of COS (Equation III) into sulfur, I require according tothe equation-. I V. 2H.s+so '=3s+2I-I 0, I additional f0. 5SO permolecule ammonium thiocyanate.

If the above quantities of; S0 are added,

' there results, that per molecule ammonium thiocyanate 2SO arerequired, which furnish 0.5+1.5=2S.

'Ihe. above proves that Equation I is covere In order to carry thisprocess through, QSO must be produced by oxidation of 2s per moleculeammonium thiocyanate. However, as just 28 are recovered in the processesm the form. of elementary sulfur, no extrane'ous sulfur at all isrequired in the process.

The conversion according to Equation I takesplace slowly at ordinarytemperature, while at C. about50 per cent of a 20 per cent solution ofNH GNS will be decom- 1 molecule tritrionate when heated, is decomposedinto 1 molecule sulfate, 1SO +1S. If igher polythionates are used, thesamecompounds will result, but in that case more sul fur is obtained,for instance in the case of tetrathionate 2S, in the case of pentathio-The equation VII thus shows that here 1 polythionate is equivalent oflS'O The equation VI further shows that by -using trithionate 4S, by theuse of tetraand pentathionate 6 and 8S respectively are obtained.

The production of polythionate, such as the trithionate from thiosulfateoccurs according to the following equation:

This reaction occurs in several intermediate steps, only one of whichhas hitherto been I ascertained. When introducing sulfur dioxide into asolution of th1osulfate,,1n contradistinction to the treatment ofthiosulfates:

with other acids no or very little sulfur will at first separate, andthe solution will remain limpid and will at the same time assume a deepyellow color. The solution now contains an additive compound of 1molecule thiosulfate and 1 molecule S0 The polythionate will form fromthese two compounds, the formation occurring slowly at ordinarytemperature and more rapidly upon heating.

1 If it is desired to produce sulfate from. thiosulfate by way of apolythionate, the simplest'method is that which follows the equation:

In order to satisfy this equation merely one-third of the thiosulfatemust be convertedinto polythionate with the aid of sul-j fur dioxide.According to equation VIII each molecule polythionate to be producedrequires 1.580 which'shows that in order to convert thiosulfate intosulfate, 0.580 must be added per molecule thiosulfate.

' Taking into consideration the equations VIII and IX, the conversion ofthiosulfate into sulfate occurs according to the equation:

The equations VI and VIII further show that a mixture of ammoniumthiosulfate and ammonium thiocyanate can be converted by means of sulfurdioxide into sulfate and sulfur accordingto the equation:

This equation shows how ammonium thiosulfate and ammonium thiocyanatecan be converted directly into sulfate and sulfur by acting with sulfurdioxide.

. I may, however, also convert ammoniumthiocyanate into sulfate andsulfur with the aid of ammonium bisulfite according to the equation.

This reaction can be explained as follows:

. As shown in equation I, 230 are required per molecule NH CNs. On theother hand a mixture of 1 molecule ammonium sulfite and 2 moleculesammonium bisulfite when heated, will also be converted into sulfate andsulfur according to the equation Now as 1NH CN S requires 2SO the doubleof the quantities shown in equation XIII must be used. The 280 are boundby the sulfite which is thus converted into bisulfite. This shows theway, in which the 8NH HSO are required according to equation XII permolecule NI'LGNS.

All these conversions of ammonium thiocyanate take place slowly atordinary temperature, more rapidly at an elevated temperature. At about100 C. about one half of the ammonium thiocyanate is decomposed withineight to ten hours, while at 180200 C. the conversion will be completedin one to two hours, all ammonium thiocyanate having disappeared.

If less sulfur dioxide, bisulfite or polythionate is used thancorresponds to the respective equations, the reaction will not becomplete and the liquor will usually still contain some ammoniumthiosulfate and nondecomposed ammonium thiocyanate. On the other hand anexcess of sulfur dioxide bisulfite or polythionate will not be harmful,the conversion being quantative and the excess of sulfur dioxide beingconverted into sulfuric acid and sulfur according to equation IV. Inthis case the liquor contains more or less sulfuric acid, which can beneutralized by adding ammonia before evaporation.

The process is preferably carried through at a temperature whichmaterially exceeds 100 C., for instance at 140-160 or above, and underincreased pressure. The ammonium thiocyanate may be contained in theliquor from the beginning. If in the purification of coal distillationgases the contents of cyanogen compounds are recovered separately underthe form of ammonium thiocyanate, bisulfite and sulfite, orcorresponding quantities of sulfur dioxide and ammonia may be added tothe solutionthus obtained.

On the other hand, if the ammonium thiocyanate is recovered in aseparate washing operation, it is also possible to force the solution ofammonium thiocyanate thus obtained, which may be preheated into theheated decomposition vessel containing an aqueous solution of bisulfiteand sulfite.

Example 1 to six hours all the thiocyanate is decomposed into sulfateand sulfur. The resulting watery solution contains 868 kgs. ammoniumsulfate. There are further obtained 168.5 kgs. pure molten sulfur and57.8 kgs. carbon dioxide, which may be tapped off.

I'may also introduce the bisulfiteg'radually during the heating period.If the reaction'is carried through at 220 0., the con-.

version will already be complete in one or two hours, while at a lowertemperature longer heating is required.

E wamgile 2 E'wample 3 A solution of 100 kgs. ammonium thiocyanate, 2083kgs. ammonium bisulfite and 610 kgs. ammonium sulfite in 2700 kgs. wateris treated as described with reference to Example 1. The watery solutionresulting in the reaction contains 2257 kgs. ammonium sulfate and thereare further obtained 337 kgs. pure molten sulfur and 57.8 kgs. carbondioxide.

Various changes may be made in the details disclosed in the foregoingspecifications without departing from the invention or sacrificing theadvantages thereof.

In the claims affixed to this specification no selection of anyparticular modification of the invention is intended to the exclusion ofother modifications thereof. I

I claim V 1. The method of decomposing thiocyanates and of producingammonium compounds therefrom. comprising heating an aqueous solution ofsuch thiocyanates in the presence of a bisulfite.

2. The method of decomposing thiocyanates and of producing ammoniumcompounds therefrom comprising heating an aqueous solution of suchthiocyanates under pressureto about 180220 C. in the presence of abisulfite.

3. The method of decomposing thiocyanates and of producing ammoniumcompounds therefrom comprising heating an aqueous solution of suchthiocyanates in the presence of a bisulfite and a sulfite.

4. The method of decomposing thiocyanates and of producing ammoniumcompounds there from comprising heating an aqueous solution of suchthiocyanates under pressure to about 180220 G. in the presence of abisulfite and a sulfite.

5. The method of decomposing ammonium thiocyanate and of producingammonium compounds therefrom comprising heating an aqueous solution ofsuch thiocyanate under pressure to about 180220 O. in the presence ofammonium bisulfite.

6. The method of decomposing ammonium thiocyanates and of producingammonium compounds therefrom comprising heating an aqueous solution ofsuch thiocyanate under pressure to about180 220 C. in the presence 0fammonium bisulfite and ammonium sulfite. In testimony whereof I affix mysignature.

CHRISTIAN J. HANSEN.

